Datasheet

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SBAS124C − DECEMBER 1999 − REVISED DECEMBER 2005
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13
A/D Converter
The 12-bit A/D converter in the ADS7870 is a successive approximation type. The output of the converter is
2s complement format and can be read through the serial interface MSB first or LSB first. A plot of output codes
vs input voltage is shown in Figure 13. With the input multiplexer configured for differential input, the A/D
transfer function is:
* 2048 v Code v 2047 for
* V
REF
G
v V
IN
v
V
REF
* 1LSB
G
With the input multiplexer configured for single-ended inputs, the A/D transfer function is:
0 v Code v 2047 for 0 v V
IN
v
V
REF
* 1LSB
G
–V
REF
+V
REF
Negative Full Scale Transition
Zero Transition
Output Code is 2s Complement
Positive Full Scale Transition
INPUT VOLTAGE
OUTPUT CODE
1000 0000 0001 (−8191)
1000 0000 0001 (−8192)
0000 0000 0010 (2)
0000 0000 0001 (1)
0000 0000 0000 (0)
1111 1111 1111 (−1)
1111 1111 1110 (−2)
0111 1111 1111 (2047)
0111 1111 1110 (2046)
Figure 13. Output Codes Versus Input Voltage
(1)
(2)